As illustrated in FIG. 14, the gravity wheel conveyor or roller conveyor is installed with a prescribed forward downslope by means of support bodies 2 and 3, and transports the object being transported 1 by gravitational operation. Therefore, the conveyor does not require any external motive power, has a simple construction, and can be used at low cost, so that it may be widely used. As is usual with a gravity conveyor, however, the transport speed of the object being transported 1 is gradually increased by gravitational operation, so that it is difficult to control the transport speed of such object, and to moderate partially or reduce the speed, or to stop such object precisely at a prescribed stop position.
Accordingly, when the gravity conveyor is in general use, a stopper 20 is disposed in a stop position (generally, the dead end position of the conveyor) as illustrated in FIG. 14, and the object being transported 1 is left to collide with the stopper 20 to come to rest. Therefore, the operator who stands in front of the conveyor and handles the object being transported has to lift and take out the object being transported, avoiding the stopper 20. This operation is bothersome and there is some worry that the object being transported may be accidentally dropped and damaged.
Furthermore, if the object being transported 1 collides with the stopper 20 just as the transport speed is gradually increased, the impact can be significant. Depending on the degree of the impact and the properties of the object being transported 1, such object itself may be ruined or damaged. For this reason, the gravity conveyor is not suitable for the transport of, for example, IC chips or the like, which are easily damaged by impact or vibration. The strength of an impact may also cause the conveyor frame 5 to vibrate and become insecure, so that the frame 5 must be firmly fixed in use.
In light of the foregoing, there are demands for a break control means that moderates and reduces the transport speed so that the object being transported 1 is stopped without violently colliding with a stopper 20.
In addition, there is a need for measures for preventing a collision by braking, or on the opposite side, accelerating the object being transported and thus increasing or decreasing the transport distance between such object so that an object that starts later does not smash against the object starting earlier in cases in which a large number of objects being transported are sequentially transported on the conveyor, or in cases in which a large number of objects are stopped on the conveyor and remain in the standby position.
To achieve the aforementioned objects, the brake apparatus for a gravity roller conveyor disclosed in the present patent document 1 is provided with a brake plate moved up and down by a hydraulic system in an intermediate position of a group of rollers arranged in two rows. The brake apparatus has a construction in which, if the object being transported on the conveyor requires braking (deceleration), the brake plate is pushed up and pressed against the passing object being transported to effect the braking action.
The brake apparatus for a gravity roller conveyor disclosed in the patent document 2 includes brake discs made of iron and fixed to the side faces of a roller that is rotatably supported by a shaft. Coil boxes are secured to the shaft detachedly from the respective brake discs with narrow spaces, and accommodate coils. The brake apparatus has a construction in which a braking force is given to the roller through the brake discs using a magnetic force produced by electrifying the coils.
In the gravity roller conveyor disclosed in the patent document 3, the outer circumferential surfaces of the rollers are formed of a special plastic layer having high hysteresis characteristics. The conveyor has a construction in which, on the premise that the kinetic energy absorbed by the special plastic layer that is compressed and deformed when the object being transported is loaded onto the rollers is greater than the energy that is released when the object being transported moves away from the rollers, the transport speed of the object being transported is reduced by the difference between the kinetic energy and the released energy.
The roller conveyor disclosed in the patent document 4 has a friction member disposed under a plurality of rollers. The conveyor is constructed such that the friction member is pressed against the rollers by inflating a rubber tube to apply braking to the rollers, and on the contrary, the rubber tube is deflated to cancel the braking.
Patent document 1: Examined Japanese Utility Model Publication No. Sho 43-17875
    Patent document 2: Examined Japanese Patent Publication No. Sho 48-38833    Patent document 3: Unexamined Japanese Patent Publication NO. Sho 55-156109    Patent document 4: Unexamined Japanese Patent Publication No. Hei 10-291616